The present invention relates to a method for forming a triple-well in a semiconductor device, and more particularly, to a method for forming a triple-well, which is suitable for simplifying the fabrication process of the semiconductor device and for increasing its integration.
In fabricating a semiconductor device, it is sometimes required that a plurality of wells are formed in a semiconductor substrate in various forms. That is, the formation of a triple-well is often required in a semiconductor substrate.
FIGS. 1A to 1E are cross-sectional views for explaining a conventional method of forming a triple-well in a semiconductor substrate.
Referring to Fig. 1A, a photoresist mask 2 is formed on a semiconductor substrate 1 through photolithography, and n-type ions such as phosphorus P are ion-implanted (3) into the substrate 1 with a high energy using the photoresist mask 2. As a result, an n-shield region 4 is formed in the substrate 1.
Referring to FIG. 1B, the photoresist mask 2 is removed and photolithography is carried out to form a photoresist mask 5 defining a certain portion of the substrate, which is narrower than the n-shield region 4. Thereafter, p-type ions such as boron B are ion-implanted (6) into the substrate 1 using the photoresist mask 5 to form a p-well 7 in the n-shield region 4.
Referring to FIG. 1C, the photoresist mask 5 is removed and then a photoresist mask 8 is formed through photolithography, which exposes a portion of the substrate 1 away from the p-well 7. N-type ions such as phosphorus P are then ion-implanted (9) into the substrate 1 using the photoresist mask 8 to form an n-well 10 separate from the p-well 7 in the substrate 1.
Referring to FIG. 1D, the photoresist mask 8 is removed and a photoresist mask 11 is formed through photolithography, which exposes a portion of the substrate 1 between the p-well 7 and the n-well 10 and a portion of the substrate 1 adjacent to the p-well 7. P-type ions such as boron B are then ion-implanted (12) into the substrate 1 using the photoresist mask 11 to form a p-well 13. Then, diffusion and annealing processes are carried out through heat treatment, and a triple-well as shown in Fig. 1E is formed in the semiconductor device.
As described above, in the conventional method for forming a triple-well, a high-energy ion implantation is carried out to form a deep n-shield region. This generates many defects in the semiconductor substrate, deteriorating the characteristic of the semiconductor device. Also, since the junction depth of the n-well and n-shield region are different from each other, it is required that the n-well and n-shield region be formed through separate ion implantation. This complicates the fabrication process.